For the fabrication of semiconductor integrated circuits, semiconductor devices are integrated and laid out in a small area of a chip, thus requiring the devices to be placed in close proximity to each other. The continued decrease in the dimensions and spacing of devices on integrated circuits requires various material layers to be deposited on the integrated circuits to electrically isolate various active components, such as transistors, resistors, and capacitors. With the inclusion of high aspect ratio features, that is, features whose height is relatively large as compared to their surface area on the chip, it becomes much more difficult to deposit isolation layers using the standard techniques currently known in the art. For example, one difficulty encountered in the deposition of isolation layers over high aspect ratio features is the formation of “voids” or “seams,” which are empty spaces between the features and the isolation layer.
One material used to form isolation layers that has proved particularly difficult to deposit over high aspect ratio features (without forming voids or seams) is silicon nitride (SixNy). Silicon nitride films are desirable as isolation layers because they exhibit excellent oxidation resistance and electrical insulating characteristics.
With the increased use of high aspect ratio features in the design of integrated circuits, there has arisen a need for methods for depositing silicon nitride films having good coverage over features having high aspect ratios, as well as films having a thin, uniform thickness. However, using conventional techniques, such as are described below, it has proven difficult to form a thin film having good coverage on substantially the entire surface of a structure having a high aspect ratio.
For example, in certain instances, conventional plasma enhanced chemical vapor deposition (PECVD) methods may be used for depositing a silicon nitride film on a semiconductor substrate. These conventional PECVD methods may include supplying a silicon source gas, e.g., silane, and a nitrogen source gas, e.g., nitrogen (N2) gas or ammonia (NH3) gas, simultaneously to a reactor in which a substrate is processed while applying radio frequency (RF) power to the reactor.
While the plasma enhanced chemical vapor deposition methods allow for deposition at a relatively low temperature with a relatively high deposition rate, silicon nitride films deposited by PECVD typically have defects, such as a high hydrogen concentration, low thermal stability, and low step coverage (i.e., poor coverage over high aspect ratio features, which undesirably leads to void and seam formation).
In another example, low pressure chemical vapor deposition (LPCVD) methods may be used for depositing a silicon nitride film. LPCVD methods may include supplying a silicon source gas, e.g., dichlorosilane (DCS), bis-tert-butylaminosilane (BTBAS), or hexachlorodisilane (HCDS), and a nitrogen source gas, e.g., ammonia (NH3) gas, simultaneously to a reactor in which a substrate is processed. The LPCVD process can be performed at a relatively low pressure of about 10 Pa to about 700 Pa and at a relatively high temperature of about 800° C. to about 900° C.
In performing low pressure chemical vapor deposition (LPCVD) in a deposition apparatus, undesirable by-products such as ammonium chloride (NH4Cl4) may be formed by a reaction between the silicon source gas and ammonia gas. Such by-products may be accumulated in the exhaust system of the deposition apparatus, leading to environmental concerns. In addition, the deposition rate using LPCVD is relatively very low, which prohibits a high throughput. Furthermore, the deposition is performed at a relatively high temperature, and thus interface oxidation (between the device and the isolation layer) may occur. Such oxidation may cause current leakage when the film is used as an insulation layer.
Accordingly, it is desirable to provide silicon nitride deposition techniques that are capable of conformal deposition over high aspect ratio features. Further, it is desirable to provide such techniques that have a relatively rapid throughput. Still further, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.